Olly - OWMC

Many people use WP as a fully fledged CMS, building sites which don’t even have a blog. In such cases, the WP comments functionality is a waste of pixels and needs completely removing. Comment Crusher was made to quickly and thoroughly clear your install of every trace of comment functionality.
For many years I have used this collection of hooks to achieve this end. So came the idea to put it in a plugin and make it available to the masses. Simply activate this plugin and never worry about comments again.
When activated, even though all pre-existing comments on your site won’t be visible, they do still exist in your database. This plugin doesn’t delete them. And so deactivating the plugin will restore full comments functionality and reveal all previous comments again.
This plugin does not collect any data, neither does it modify your database.
<ul>
<li>Disable comment and trackback support from all post-types</li>
<li>Deactivate comments and pings on the front end</li>
<li>Hide all existing comments</li>
<li>Remove the comment metabox from the dashboard</li>
<li>Remove comments link from the toolbar</li>
<li>Remove the admin menu link for comments</li>
<li>Redirect anyone trying to access the comments admin page </li>
</ul>
This plugin was built using the <a href="https://wppb.me" rel="nofollow ugc">WP Plugin Boilerplate</a> and the custom functionality code I think goes back to <a href="https://gist.github.com/mattclements/10a997775894c7a0eba1" rel="nofollow ugc">Matt Clements in 2013</a>.

Comment Crusher

Disable and remove comments on your WP site.

WP Chill

Silkalns

Cristian Raiber

A very useful plugin for everyone using WordPress. Adds reCaptcha security to the WordPress login form, register form and comment form. This plugin could help your blog get rid of a lot of spam comments or brute-force attacks.
Nothing gets passed it if the reCaptcha doesn’t validate.
A few notes about the plugin:
<ul>
<li>Supports audio or image captcha types</li>
<li>Can generate the reCaptcha image / audio type in a number of predefined languages</li>
<li>Adds reCaptcha protection to the WordPress login form</li>
<li>Adds reCaptcha protection to the WordPress register form</li>
<li>Adds reCaptcha protection to the WordPress comment form</li>
<li>Adds reCaptcha protection to the WordPress recover password form</li>
</ul>

Uber reCaptcha

This plugin adds the reCaptcha form to the WordPress login form, recover password form, register form and comment form.

Comment Crusher vs Uber reCaptcha